Cardiovascular disease is the leading cause of death in the United States. A number of methods have been developed for treating coronary heart disease. One common procedure is percutaneous transluminal coronary angioplasty ("PTCA"). PTCA typically involves advancing a catheter, having an inflatable balloon on the distal end thereof, through a patient's arterial system until the balloon crosses an atherosclerotic lesion. The balloon is then inflated to dilate the artery. After dilation, the balloon is deflated and the catheter removed leaving an enlarged arterial passageway or lumen, thereby increasing blood flow. A significant number of PTCA procedures, however, result in a restenosis or renarrowing of the lumen.
To lessen the risk of stenosis or restenosis of lumens, various endovascular devices have been proposed for mechanically keeping an affected lumen open after completion of procedures, such as PTCA. For purposes of the instant invention, the lumen to be treated is not limited to coronary arteries, but also includes any other similar body conduit that tends to improperly constrict as a result of disease or malfunction, such as: arteries located within the mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes.
Endovascular devices generally referred to as "stents," and covered endovascular support devices generally referred to as "stent-grafts," are typically inserted into the lumen, positioned across a lesion, and then expanded to keep the passageway clear. Effectively, the stent or stent-graft overcomes the natural tendency of some lumen walls to close due to restenosis, thereby maintaining a more normal flow of blood through that lumen than would be possible if the stent or stent-graft were not in place or if only a PTCA procedure were performed.
There are two general categories of stents, self-expanding stents and balloon-expandable stents. Some self-expanding stents are made from stainless steel wire or wire braid. Such stents are typically compressed into a first shape and inserted into a sheath or cartridge. During insertion, the stent is positioned along a delivery device, such as a catheter, that is extended to make the stent diameter as small as possible. When the stent is positioned across the lesion, the sheath is withdrawn causing the stent to radially expand and abut the vessel wall. Depending on the materials used in construction of the stent, the wire or wire braid maintains the new shape either through mechanical force or otherwise.
Another type of self-expanding stent is made from a shape-memory alloy such as NITINOL. This stent has been pre-treated to assume an expanded state at body temperature. Prior to delivery to the affected area, the stent is typically crimped or compressed near or below room temperature.
Balloon-expandable stents are typically introduced into a lumen on a catheter having an inflatable balloon on the distal end thereof. When the stent is at the desired location in the lumen, the balloon is inflated to circumferentially expand the stent. The balloon is then deflated and the catheter is withdrawn, leaving the circumferentially expanded stent in the lumen, usually as a permanent prosthesis for helping to hold the lumen open.
One type of balloon-expandable stent is a tubular-slotted stent, which involves what may be thought of as a tube having a number of slots cut in its wall, resulting in a mesh when expanded. A tubular-slotted stent is typically cut out of a hypo-tube, or out of a sheet, which is then rolled, and welded to form a the tube. Example of such stents include, but are not limited to, those disclosed in U.S. Pat. Nos. 4,733,665, 4,776,337, 4,739,762 and 5,102,417 all issued to Palmaz, U.S. Pat. No. 5,195,984 issued to Schatz, U.S. Pat. No. 5,421,955 issued to Lau et al., or U.S. Pat. No. 5,449,373 issued to Pinchasik et al.
A balloon-expandable stent referred to as a wire stent overcomes some of the problems associated with tubular-slotted stents. A wire stent is generally formed by winding a circular shaped wire into supportive elements, which typically have a circular cross-section. The problem with wire stents is that the supportive elements comprising the stent can axially displace with respect to each other, resulting in a stent that fails to provide adequate support.
U.S. Pat. Nos. 5,292,331 and 5,674,278 both issued to Boneau, which are hereby incorporated by reference, disclose another type of wire-like stent. This stent is made by taking a ring or toroid having a circular cross-section, and then forming the ring into a series of sinusoidally-shaped elements. While preferably employing a single piece of material, suitably welded wire is also acceptable. Such a stent has excellent radial strength while retaining the flexibility of wire stents. This endovascular support device may include a plurality of stents mounted on the balloon.
All these stent can be used alone or in conjunction with a covering or graft.
During a PTCA procedure as discussed above, atheromatous plaques undergo fissuring, thereby creating a thrombogenic environment in the lumen. Excessive scarring may also occur following the procedure, potentially resulting in reocclusion of the treated lumen. Attempts to address these problems include providing a suitable surface within the lumen for more controlled healing to occur in addition to the support provided by a stent. These attempts include providing a lining or covering in conjunction with a stent. The covering of a stent-graft may prevent excessive tissue prolapse or protrusion of tissue growth through the interstices of the stent while allowing limited tissue in-growth to occur to enhance the implantation. The surface of the graft material at the same time minimizes thrombosis, prevents scarring from occluding the lumen and minimizes the contact between the fissured plaque and the hematological elements in the bloodstream.
The stents, and stent-graft, assemblies are mounted on a balloon of a balloon catheter and forcibly expanded from pressure exerted during expansion of the balloon, as discussed above. These stents and stent-grafts are circumscribe most but not all of the length of the balloon. The exposed ends of the balloon, coupled with the fact that the ends of the stent or stent-graft will inherently deploy under less force than the medial portion thereof, results in the stent or stent-graft being deployed in a non-uniform fashion. More specifically, the ends of the stents begin to deploy prior to the reminder of the stent.
Further, with regard to prior art stent-grafts, much focus has been directed towards adhering or attaching the graft material to the stent.